Three comments: 1. I presume you increase you exposure dose for the second layer? If you don't you will underexpose the second layer due to the lower reflection from the substrate. Try increasing the exposure dose by 50% and see what happens. 2. For your second layer your thermal gradient is considerably lower than for the first layer, due to the thermal isolation of the first layer. I presume you use a hotplate for the soft-bake. Try increasing the bake time, but don't increase temperature beyond 115 C as the SU-8 will autocrosslink at higher temperatures. 3. For your PEB you can try baking at 35 C overnight before doing you normal PEB. The trick is to cause the SU-8 to crosslink sufficiently below the Tg of un-crosslinked SU-8 (50 C). If you exceed the Tg before it has crosslinked sufficiently, it will flow and then crosslink in the distorted shape. Regards Jacques Jonsmann ________________________________ Fra: mems-talk-bounces@memsnet.org p=E5 vegne af Shao Guocheng Sendt: ti 02-12-2008 03:19 Til: General MEMS discussion Emne: Re: [mems-talk] very thick layer of SU-8 Hi, All: So what kinda softbaking process u guys using for ultra-thick SU-8 layer. I'm working with 1mm thick SU-8. My process is: Spincoating first layer(around 500um), softbake at 65C for about 2 hours and slowly ramp to 110c, hold for 6 hours and slowly ramp to room temp. for the first layer I can bake out aroun 28% of the solvent which SU-8 50 should have 31%. But the remaining 3% seems not a big problem and I can finish my first layer exposure pretty well. for the second layer, I use almost the same process, but hold at 110c for 8hr, but I can only bake out around 24% of solvent. Because of that, during my PEB process, severe wrinkle happen around 50-60C, although it will smooth out after a while, some of my fine structures r destorted by these wrinkles. I tried to lower the baking temperature to 90C and bake for 15hrs, but still, only 24%-25% of solvent can be bake out. Any one has a cure for this prolem? thx a lot Guocheng Shao